1. Field of the Invention
This invention relates to a chamfering pressing machine for chamfering and shearing materials, such as a metal sheet of coil-like stock, to form uniform products of a particular shape.
2. Discussion of the Related Art
A conventional chamfering pressing machine, as shown in FIG. 7, comprises a chamfering die 20 and a chamfering punch 21, and uses a coil-like stock 22. Springs 28a of a stripper 28 forces the coil-like stock 22, subjected to a shearing operation, toward the chamfering punch 21.
The coil-like stock 22 is fed by a feed device (not shown), such as a roll feeder, in the direction of arrow A as shown in FIG. 6, and is subjected to various operations. First, a chamfered portion 23 is formed by the chamfering die 20 and the chamfering punch 21, and then holes 24 are formed. Subsequently, a product 25 having a chamfered portion 25a and holes 24 is formed by a shearing operation through a blanking die 26 and a blanking punch 27. In order to form the product 25 by shearing, holes 24 are used as positioning means, and from this position, the chamfered portion 23 is sheared. Therefore, as shown in a lower portion of FIG. 6, the chamfered portion 25a is formed on one edge of the product 25.
However, such a conventional chamfering pressing machine has the following problems:
(1) The chamfered portion 23 is formed in the coil-like stock 22, and therefore, even if the chamfered portion 23 is formed uniformly, the thickness of the chamfered portion 25a of the product 25 becomes uneven because of backlash formed in a take-up holder portion for the coil-like stock 22 and in the positioning means provided by the holes 24. As a result, the position of the chamfering punch 21 must be adjusted frequently.
(2) As shown in an enlarged scale in FIG. 8, when the chamfered portion 23 is formed by the chamfering die 20 and the chamfering punch 21, one side of the coil-like stock 22 is restrained by the positioning means provided by the holes 24, and the other side thereof is restrained by the taken-up or rolled portion of the coil-like stock 22. Therefore, the squeezed or pressed material of the stock cannot escape anywhere. As a result, a high working pressure is required.
(3) When the chamfered portion 23 is formed by the chamfering die 20 and the chamfering punch 21, in the vicinity of the chamfering punch 21, the material of the stock is raised in the direction of the thickness of the stock and moved in the feed direction A, as indicated by arrows in FIG. 8, to cause deformation and adversely affect the flatness of the product 25.
(4) When the chamfering punch 21 and the blanking punch 27 are disposed close to each other as shown in FIG. 7, a space for accommodating these punches can be reduced; however, since the directions of movement of the two punches 21 and 27 are opposite, the coil-like stock 22 is undesirably bent or deformed, thereby adversely affecting the flatness of the product 25.